This invention relates to an improved wood preservation process for the pressurized treatment of wood. The invention relates further to products treated by the same process.
A variety of processes and chemicals have been used to treat wood for preservation purposes. Illustrative U.S. patents showing known techniques and materials for the treatment of wood are U.S. Pat. Nos. 1,203,038, 2,517,580, 3,839,052, 3,889,025, 4,267,082, 4,637,952, 4,649,065, 4,923,760, 4,927,672, 5,013,748, 5,824,370, 6,123,756, 6,174,947B1. Many of these methods relate solely to surface treatments. Others relate to carriers or additives that have biocidal or other preservative functions.
Some conventional wood preservation techniques used for wood bearings, utility poles, railroad ties, landscape timbers, docking and marine structures, etc., rely on the impregnation of the wood with a liquid that may be a preservative or that may be a carrier doped with additives. Additives may be selected as appropriate for preservation in a selected environment (e.g. heavy metals and/or organic or inorganic substances such as copper naphthenate, or other wood preservatives used to repel animals such as rodents, to deter encrustation in marine environments, to deter the growth of bacteria, fungi, etc., or to protect the wood from other environmental factors). The liquids typically remain fluid even after they are forced into the wood and thus are prone to leakage from the wood. Also, chemical constituents of the preservative material may leech from the wood and, thus, be present on the surface of the treated wood.
Some of the preservatives used in the treatment of wood have chemical constituents that are toxic, carcinogenic and/or are not biodegradable. One of the most prevalent preservative agents in treated wood is Chromated Copper Arsenate (CCA) which contains arsenic a known carcinogen. Recently, the United States Environmental Protection Agency in cooperation with industry has adopted regulations that would prohibit the use of CCA treated wood from all residential applications including play-structures, decks, picnic tables, landscaping timbers, residential fencing, patios, walkways, boardwalks, and wood edging.
In addition to CCA treated wood, industry also currently uses a Copper Boron Azole (CBA) preservative. The active ingredients in copper azole are copper and tebuconazole. Copper azole is an EPA registered pesticide. Exposure to copper azole may present certain hazards as some chemical may migrate from the wood to the surrounding soil over time or may be dislodged from the wood surface upon contact with the skin. Another preservative used by the wood industry is Ammonia Copper Quaternary (ACQ).
The toxicity of the chemical preservatives, coupled with the constant leakage of the preservative material or leeching of constituents of the preservative to the surface of the treated wood and into the surrounding area may have adverse environmental, health, and/or infrastructure impacts. The current invention avoids all of these concerns when used without any pesticides and antifungal additives. Of course, pesticides and antifungal additives, or other additives, may be used with the current invention in applications where the treated wood would be exposed to adverse use conditions, or to promote the impregnation of the oil into the wood.
In addition to possible environmental risks and poor preservation performance, the low viscosity nature of typical wood preservative impregnation fluids causes additional labor and maintenance for the upkeep of material stocks. For example, when stored horizontally, wood pieces such as utility poles and railroad ties need to be turned periodically to prevent the fluid in the wood from being forced down and out of the wood by gravity. Further, fluid migration may leave installed wood products unprotected, as may be seen in telephone poles wherein the impregnated fluid has migrated downward and left the top dry and vulnerable. There is therefore a need for an improved wood preservation technology wherein carriers and additives in the carrier are less susceptible to migration from the wood that is being preserved. There is a further need for an improved wood preservation technology wherein the carrier itself is an environmentally friendly material. Finally, there is a need for an improved wood preservation technology wherein the carrier is an inexpensive material.
It has been discovered that polymerized soybean oils are especially effective in the pressurized treatment of wood products. In application, it has been determined that unrefined and refined soybean oil may be used. Further, it has been found that both the crude oil from genetically modified soybeans or and the crude oil from non-genetically modified soybeans is suitable for use. The method of preservation and the wood products that employ soybean oil preservation are advantageous because the soybean oil is more environmentally friendly; it is not toxic; and the use of polymerized soybean oil results in improved sequestration of the soybean oil and of any additives carried by the soybean oil to the interior of the treated wood.
The method of the present invention involves the application of soybean oil to wood under a pressure regime to drive the soybean oil into the wood. This preservative infusion process is well known to the industry. The pressure regime may involve the selective application of vacuum. The method further involves the promotion of polymerization of the soybean oil in-situ to increase viscosity and thereby fix the oil and any additives carried by the oil within the wood to prevent or minimize later leakage. Depending on the application and the potential detrimental effects of selected additives, it may be desired to promote a greater degree of polymerization throughout the wood to fully solidify the soybean oil or it may be desired to allow the soybean oil within the wood to remain slightly fluid and to promote or apply a more fully polymerized layer of soybean oil at the surface of the wood which solidifies to encapsulate the wood.
Of note, if the present invention is practiced to achieve a partially polymerized soybean oil followed by a more polymerized coating, a self-sealing characteristic is now present with the treated wood. This self-sealing characteristic is based upon a known property of soybean oil, namely a general lack of oxidative stability. When the outer coat of the wood treated with soybean oil is breached, the less fully polymerized soybean oil retained in the interior migrates to the surface. As it reaches the surface, it is exposed to the air where oxidation begins which will result in the solidification of the soybean oil (polymerization).
Depending on the application, the selected pressure chamber and pressure regime, and the wood to be preserved (density, pore size, etc.), it may be desired to prepare the soybean oil in advance of impregnation in order to initiate polymerization.